1. Field of the Invention
The present invention relates to a multiprocessor-type one-chip microcomputer storing a plurality of processors and a plurality of ROMs connected to a system bus provided for each processor and arranged in separate memory spaces.
2. Description of the Prior Art
FIG. 6 shows a system block diagram of a general multiprocessor. In FIG. 6, symbol 1 is a first CPU (A), 2 is a RAM (A) corresponding to the first CPU (A) 1, 10 is a ROM (A) corresponding to the first CPU (A) 1, and 4 is a system bus (A) for connecting the first CPU (A) 1, RAM (A) 2, and ROM (A) 10. Symbol 5 is a second CPU (B), 6 is a RAM (B) corresponding to the second CPU (B), 11 is a ROM (B) corresponding to the second CPU (B) 5, and 8 is a system bus (B) for connecting the second CPU (B) 5, RAM (B) 6, and ROM (B) 11. A first system comprises the CPU (A) 1, RAM (A) 2, ROM (A) 10, and system bus A) 4, and a second system comprises the CPU (B) 5, RAN (B) 6, ROM (B) 11, and system bus (B) 8.
The following is the description of operations of the multiprocessor.
The CPU (A) 1 reads a program from the ROM (A) 10 to execute processing, which uses the RAM (A) 2 as a working space for temporarily storing data during processing as necessary. Also, the CPU (B) 5 uses the ROM (B) 11 and RAM (B) 6 to execute processing. Moreover, information is transferred between both processings by communication means 9 as necessary. The communication means 9 is generally realized with a shared memory (e.g. dual port RAM) and a serial interface.
Therefore, because two types of processings are executed simultaneously, advantages are produced that the processing speed can be improved and a program can be developed through functional sharing.
As shown in FIG. 6, a multiprocessor-type one-chip microcomputer made by forming two systems on one chip has been used in recent years. However, a mask ROM is frequently used as a stored ROM because it is difficult to use a programmable ROM (hereafter referred to as PROM) for the stored ROM because the number of writing terminals increases. That is, when the PROM is used as the stored ROM, several tens of terminals are newly required as the terminals for two PROM writing buses (including address and data buses). However, the above constitution is very difficult for practical use because a multiprocessor-type one-chip microcomputer originally has many terminals. Therefore, the mask ROM is used for the stored ROM. In this case, to develop a program, it is necessary to form the system bus (A) 4 and system bus (B) 8 outside the chip in order to connect a PROM in which a program is written because a program before debugging is written in the PROM by using a .FROM writer to perform an operation test using an actual microcomputer. These terminals are unnecessary for normal use, that is, when only the stored ROM is used. Therefore, it is necessary to prepare an evaluation chip for program development. Concretely, as shown in FIG. 7, an evaluation chip is prepared on which additional terminals 4a and 8a for forming the external system bus (A) 4 and external system bus (B) 8 are provided and PROMs 10a and 11a in which a program is written are connected to the additional terminals 4a and 8a to repeat the test and debugging.
Because the existing multiprocessor-type one-chip microcomputer is constituted as shown above, It is necessary to separately develop a special chip for program development. Moreover, the special chip for program development has problems that many additional terminals are necessary, the shape of the chip is frequently different from that of an IC normally used, and the burden for a user to use the special chip for program development increases.